Apparatus for the improvements in thermostats or heat controls



APIII 5, 1955 c. H. STRANGE 2,705,746

APPARATUS FOR THE IMPROVEMENTS TN THERMOSTATS, 0R HEAT CONTROLS su, 195s Ila lla. ,Ax man y' I Y p fl; I

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1N VEN TOR. @H4/PL .es H. STAM/veg wia /4 am? f7 7" T'ORNEY United States Patent() APPARATUS FOR THE IMPROVEMENTS IN THERMOSTATS OR HEAT CONTROLS Charles H. Strange, Jacksonville Beach, Fla., assignor to Elsa L. Strange, Jacksonville Beach, Fla.

Application October 30, 1953, Serial No. 389,278 1 Claim. (Cl. 200-137) This invention relates to improvement in thermostats or heat controls for the maintenance of temperatures of the order of from l500 F. to 2400 F. and is related to apparatus for similiar purposes described in my copending application Serial Number 330,195, filed January 8, 1953.

deteriorate with use. Furthermore the use of thermocouples requires delicate operating conditions which quite often are disturbed by the magnetic leld when induction heating is employed.

An object of the invention is to provide relative-expansion members which are operative at the above temerature range and which are not adversely affected by oven or kiln contents thereat.

Another object is to provide for the operation of a simple switch by the expansion of one member relative to that of another.

Still another object is to provide a thermostat that is economical to produce, has a minimum of moving parts and which may be produced largely from stock parts and yet be long lived and reliable in operation.

For the attainment of these and other objects, I employ two longitudinal coaxial expansion members, one within the other, one of said members being non-metallic refractory material, and the other being of metal having a higher coeicient of thermal expansion than that of the refractory material, and means responsive to the relative expansion of the two members for making and breaking an electric current.

In the accompanying drawing showing, by way of example, two of many possible embodiments of the invention,

Figure 1 is a longitudinal sectional view of one form of the invention,

Figure 2 is a similar view of another form of the invention, and Figure 3 is a fragmental detail of a modication of the invention.

'I'he invention according to Figure 1 comprises outer and inner coaxial longitudinal members and 11 one within the other, the inner member being of refractory non-metallic material such as quartz, porcelain, Alundum (aluminum oxide) or other ceramic material having a low rials met with in kilns or ovens when operating at temperatures up to the order of 2400 F., a suitable metal being Inconel an alloy melting at about 2500 F. composed of approximately 79.5% Ni, 13% Cr, 6.5% Fe, 0.25% Mn, 0.25% Si, 0.20% Cu, 0.08% C. This metal has a coeicient of expansion of about 0.64)(10r5. Another and still more suitable metal is known to the trade as Kanthall, whch has similar properties to those of Inconel, but softens at temperatures about 250 F. higher than does Inconel and is composed of approximately C, 0.25% max.; Si, 0.32.0%; Cr, 18-25%; Al, 3.56.5%; Co, 0-3.0%; Ta, 030%; Mn, O.2-l.0% and the balance Fe. While the coeicient of expansion of these metals (nil) to enable appreciable relative movement of the two members.

2,705,746 Patented.` Apr. 5, 1955 ICC T eamembers are preferably of cylrndrical shape so that the tube 10, the two tubes being joined end-to-end as by In use, the support is disposed in and through a hole 20 in a kiln or oven wall or top 21 so that the members 10 and 11 project into the interior of the kiln. For best results the members lll) and 11 should be about 8 inches long.

A housing 22 is secured fast to the opposite end 24 of the support tube by means of a plate and sleeve piece 25 secured to the tube 18 by means of threads 26 and screws, such as at 27, securing the piece 25 to the forward wall 28 of the housing.

Within the support tube 18 is a rod or other suitable longitudinal member 29 slidable, over its entire length, relative to the tube 18. The outer end 30 of the rod 29 is urged against the inner end 16 of the refractory member 11 in a manner to be described below. Preferably, the support tube 18 and the rod 29 therein are of the same material so that any heat absorbed from the kiln by distance screws 3 8. The spring 32 keeps the end 30 By having the outer member 10 of metal the time lag 1n lts temperature changes relative to those of the contents of the kiln are minimized and the thinner the walls and switch may be selectively determined by an adjusting screw 45 mounted on the housing 221. A tension spring 46 keeps the switch bracket urged against the end of the screw in a known manner. Indicia (not shown) on a dial 48 associated with a knob and pointer 49 on the screw aiord a means for indicating the position of the switch 40 and button 44 in a well known manner.

Since a lowering temperature causes the rod end 35 to move toward the button44, a shutting off of the heat to the oven, when the switch is positioned to maintain a temperature of say l800 F., the rod 29 might force the button 44 into the switch an excessive distance as the temperature falls to that of the room. To overcome this effect I provide a slidable cap 50 over the end portion 35 and cushion it with a compression spring 51. A twelve ounce spring 51 works satisfactorily when a four ounce force is necessary to actuate the button 44.

The relative expansion members may be reversed in a manner somewhat similar to the arrangement shown in my above mentioned co-pending application, as in Figure 2 wherein the metal member 10a, of material described of member 10, is a rod of length comparable to that of the tube and disposed within a refractory tube 11a. Tube 11a is preferably a continuous tube comparable in length to that of the tubes 10 and 18 combined, but rod 10a stops short of the kiln wall 21 as at 16a so as not to be aifected by the wall temperatures. Motion of the rod and 16a is transmitted to the interior of the housing 22 by a refractory rod 29a having nil expansion. The sleeve and plate piece 25, instead of being threaded on to the refractory tube is secured on to a sleeve 24a firmly holding the refractory tube through the medium of asbestos packing 23a. The outer end 37a of rod 29a terminates short of the end of the refractory tube and a metal end portion a similar to ithat described in Figure 1 is held against the end 37a in the manner previously described of Figure 1 It will be noticed that 'an increase or decrease in temperature has opposite effects on the protrusion of end portions irl-Figures 1 and 2. However the openings of the micro switch 40 may be employed to increase or decrease the heat supply in a known manner according to whether the apparatus of Figure 1 or that of Figure 2 point of the iicient of thermal expansion is used. The threading of screw or the calibration of the dial 48 may be chosen so as to rectify temperature settings according to the apparatus used.

Especially in the construction shown in Figure 2 may the cap 50 and spring 51 be omitted and it has even been found that they may bev omitted from the construction of Figure 1 though the device inthe latter form with cap and spring omitted has been tested over only a relatively short length of time'so vits reliability in terms of months of service is not known-as is truel of the construction shown in my co-pending application referred to above. Thus as shown in Figure 3 the end face 43 of the end portion 35 may engage directly the button 44.

The -apparatus of both main forms is lubricated with talc or powdered soapstone to enable free movement of the various elements. This material not only serves as a lubricant but is especially beneficial in the invention of Figure 2 to minimize diffusion of harmful gases into the annular space between the metal hot rod 10a and the tube 11a which creep in through the outer end of the tube. Of course as the system cools these gases are drawn further into the tube but at low temperature they are not troublesome. They can even then be expelled by an alternate heating and cooling at a safe low temperature in an atmosphere of inert gas.

I have found that a junction of Inconel and Kanthall, identified as to composition above, may be used as a substitute for a similarly formed conventional platinum-rhodium junction for use in thermocouples at temperatures up to about 2400 F. The millivolt potential over a temperature range up to near the fusion InconelKanth`all junction varies from that of the Pt-Rh only about 2 or 3 per cent at the same temperatures and the metals are much cheaper than platinum and rhodium.

The invention claimed is:

In a thermostat, inner and outer cylindrical members longitudinal and coaxial, one within the other, the outer member being of refractory non-metallic material substantially unaffected by temperatures as high as 2400" F., the inner member being of metal having a higher coefthan that of the refractory material and infusible at said temperatures, an end portion of one member being limited against movement relative tothe other, and powdered soapstone between the inner Aand outer members for decreasing friction therebetween-*and to reduce diiusion of gases toward the`V inner member, a switch having a button substantially coaxial with said members, and means substantially coaxial with the button and members for transmitting relative longitudinal movement of one end of a member relative to another.

References Cited in the ile of this patent UNITED STATES PATENTS 

